Android:无法打开文件磁盘空间不足

我有一个应用程序，用于读取和保存xml文件，并在internet连接可用时写入该文件，否则它将读取已保存在终端上的文件

WriteFeed函数：

// Method to write the feed to the File
            private void WriteFeed(RSSFeed data) {

                FileOutputStream fOut = null;
                ObjectOutputStream osw = null;

                try {
                    fOut = openFileOutput(fileName, MODE_PRIVATE);
                    osw = new ObjectOutputStream(fOut);
                    osw.writeObject(data);
                    osw.flush();
                }

                catch (Exception e) {
                    e.printStackTrace();
                }

                finally {
                    try {
                        fOut.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }

// Method to read the feed from the File
            private  RSSFeed ReadFeed(String fName) {

                FileInputStream fIn = null;
                ObjectInputStream isr = null;

                RSSFeed _feed = null;
                File feedFile = getBaseContext().getFileStreamPath(fileName);
                if (!feedFile.exists())
                    return null;

                try {
                    fIn = openFileInput(fName);
                    isr = new ObjectInputStream(fIn);

                    _feed = (RSSFeed) isr.readObject();
                }

                catch (Exception e) {
                    e.printStackTrace();
                }

                finally {
                    try {
                        fIn.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }

                return _feed;

            }

WriteFeed函数：

// Method to write the feed to the File
            private void WriteFeed(RSSFeed data) {

                FileOutputStream fOut = null;
                ObjectOutputStream osw = null;

                try {
                    fOut = openFileOutput(fileName, MODE_PRIVATE);
                    osw = new ObjectOutputStream(fOut);
                    osw.writeObject(data);
                    osw.flush();
                }

                catch (Exception e) {
                    e.printStackTrace();
                }

                finally {
                    try {
                        fOut.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }

// Method to read the feed from the File
            private  RSSFeed ReadFeed(String fName) {

                FileInputStream fIn = null;
                ObjectInputStream isr = null;

                RSSFeed _feed = null;
                File feedFile = getBaseContext().getFileStreamPath(fileName);
                if (!feedFile.exists())
                    return null;

                try {
                    fIn = openFileInput(fName);
                    isr = new ObjectInputStream(fIn);

                    _feed = (RSSFeed) isr.readObject();
                }

                catch (Exception e) {
                    e.printStackTrace();
                }

                finally {
                    try {
                        fIn.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }

                return _feed;

            }

我有足够的磁盘空间，有时我会得到“MemoryCach将使用高达16 Mb的内存”，总是会得到“磁盘空间不足，无法索引”和“FeatureCode>无法打开文件”

我的应用程序出了什么问题